Reread some of the comments.
In gear, going down a hill, there is no load on the engine. In fact, the transmission is able to keep the engine turning just because of the force of gravity on the car going down hill. Since the transmission is turning the engine, the computer turns off all of the fuel injectors and no fuel at all is used while the car is coasting down the hill. The injectors would only be turned on if you pushed the gas pedal.
However, out of gear, the transmission can’t turn the engine. The computer has to turn the fuel injectors on to keep the engine running, so it uses whatever fuel it would normally use at idle.
Coasting in gear = no fuel used at all.
Coasting out of gear = same amount of fuel used as when idling.